Microwave-assisted magnetic recording head with high saturation magnetization material side shield

ABSTRACT

Approaches to improving the signal-to-noise ratio in a microwave-assisted magnetic recording hard disk drive over the entire region from the inner diameter to the outer diameter of the disk, especially in the context of shingled magnetic recording, include a narrower side gap on the side opposing a spin torque oscillator offset direction than the side gap in the offset direction, thereby increasing the gradient of the recording magnetic field in the cross-track direction and reducing the track edge noise of the recording pattern. Embodiments include use of a side shield on the side opposing the offset direction that has a higher saturation magnetization than the side shield on the side in the offset direction, thereby further increasing the gradient of the recording magnetic field in the cross-track direction.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a division of and claims the benefit of priority toU.S. patent application Ser. No. 14/042,459 filed on Sep. 30, 2013, theentire content of which is incorporated by reference for all purposes asif fully set forth herein.

FIELD OF THE INVENTION

Embodiments of the invention relate generally to magnetic recording andmore particularly to improving the signal-to-noise ratio in a hard diskdrive.

BACKGROUND

A hard-disk drive (HDD) is a non-volatile storage device that is housedin a protective enclosure and stores digitally encoded data on one ormore circular disks having magnetic surfaces. When an HDD is inoperation, each magnetic-recording disk is rapidly rotated by a spindlesystem. Data is read from and written to a magnetic-recording disk usinga read/write head that is positioned over a specific location of a diskby an actuator.

A read/write head uses a magnetic field to read data from and write datato the surface of a magnetic-recording disk. Write heads make use of theelectricity flowing through a coil, which produces a magnetic field.Electrical pulses are sent to the write head, with different patterns ofpositive and negative currents. The current in the coil of the writehead induces a magnetic field across the gap between the head and themagnetic disk, which in turn magnetizes a small area on the recordingmedium.

Increasing areal density (a measure of the quantity of information bitsthat can be stored on a given area of disk surface) is one of theever-present holy grails of hard disk drive design evolution, and hasled to the necessary development and implementation of various means forreducing the disk area needed to record a bit of information. It hasbeen recognized that one significant challenge with minimizing bit sizeis based on the limitations imposed by the superparamagnetic effectwhereby, in sufficiently small nanoparticles, the magnetization canrandomly flip direction under the influence of thermal fluctuations.

Microwave-Assisted Magnetic Recording

“MAMR” refers to “microwave-assisted magnetic recording”. Using MAMR,the head slider emits a microwave field that excites the electrons inthe media, building up energy that eases and assists the process ofwriting data bits. The MAMR process is likely to use a localized highfrequency magnetic field generated by a magnetic thin film stackintegrated into the head sliders. One technique for implementing such afilm stack utilizes a spin torque oscillator (STO). The STO elementinjects auxiliary magnetic flux to the write pole to facilitate themagnetization switching of the write pole, where electrical current tothe STO induces rotation of the magnetization of a free ferromagneticlayer in the STO, which generates the auxiliary magnetic flux. Applyingthis AC magnetic field to the media reduces the coercivity of the media,thereby facilitating high-quality recording.

Shingled Magnetic Recording

A shingled magnetic recording (SMR) system is another recording methodfor improving areal density. SMR can obtain high surface density withoutreducing the strength of the recording magnetic field by using arecording head which is wider than the track pitch. With SMR, duringrecording of a given track, the track is recorded while overwriting oneside of the adjacent recording pattern that has already been recorded.Recording tracks are successively formed while always overwriting therecording pattern on the same side. As a result, the effective recordingtrack width in the SMR system is the width of the recording patternformed by the recording head, less the width of the portion which hasbeen overwritten and deleted by the adjacent track. Therefore, the widthof the main pole of the recording head in the SMR system need not matchthe width of the recording track, and a recording head having a widerpole width than the effective recording track width can be used.Consequently, sufficient writing capacity can be obtained even with anarrow effective track width and, as a result, a higher track densitycan be realized and a higher areal density can be obtained.

Combining MAMR and SMR, i.e., combining an STO with a pole having a widewidth, can be expected to obtain even higher surface recording density.However, conventional combinations of MAMR and SMR do not necessarilyobtain an improvement in the SNR (signal-to-noise ratio) by MAMR overthe entire region from the inner to the outer diameter of the disk.

SUMMARY OF EMBODIMENTS OF THE INVENTION

Embodiments are directed to a microwave-assisted magnetic recording(MAMR) head design having a side shield on the side opposing the offsetdirection that has a higher saturation magnetization than the saturationmagnetization of the side shield on the side in the offset direction,thereby increasing the gradient of the recording magnetic field in thecross-track direction.

Embodiments include a wrap-around shield (WAS) that wraps around aportion of the main pole, gaps between the main pole and the WAS, and aspin torque oscillator (STO) positioned between the main pole and atrailing portion of the shield and offset in a particular lateraldirection from the centerline of the main pole. The side gap on the sideopposing the offset direction is narrower than the side gap in theoffset direction, thereby increasing the gradient of the recordingmagnetic field in the cross-track direction and reducing the track edgenoise of the recording pattern.

Embodiments discussed in the Summary of Embodiments of the Inventionsection are not meant to suggest, describe, or teach all the embodimentsdiscussed herein. Thus, embodiments of the invention may containadditional or different features than those discussed in this section.

BRIEF DESCRIPTION OF THE DRAWINGS

Embodiments of the invention are illustrated by way of example, and notby way of limitation, in the figures of the accompanying drawings and inwhich like reference numerals refer to similar elements and in which:

FIG. 1 is a plan view of a hard disk drive (HDD), according to anembodiment of the invention;

FIG. 2 is an air bearing surface (ABS) view of a shingled magneticrecording (SMR) head having a spin torque oscillator (STO), according toan embodiment of the invention;

FIG. 3 is a schematic diagram illustrating the arrangement of arecording track and write head when using an SMR head having a STOconfigured as in FIG. 2, at (a) an inner diameter region, (b) a middlediameter region, and (c) an outer diameter region, according to anembodiment of the invention;

FIG. 4 is an ABS view of an SMR head having an STO, according to anembodiment of the invention;

FIG. 5 is a diagram illustrating the arrangement of a recording trackand write head when using an SMR head having an STO as illustrated inFIG. 4, at (a) an inner diameter region, (b) a middle diameter region,and (c) an outer diameter region, according to an embodiment of theinvention;

FIG. 6 is an ABS view of an SMR head having an STO, according to anembodiment of the invention;

FIG. 7 is a diagram illustrating the arrangement of a recording trackand write head when using an SMR head having an STO as illustrated inFIG. 6, at (a) an inner diameter region, (b) a middle diameter region,and (c) an outer diameter region, according to an embodiment of theinvention;

FIG. 8 is an ABS view of an SMR head having an STO, according to anembodiment of the invention; and

FIG. 9 is an ABS view of an SMR head having an STO, according to anembodiment of the invention.

DETAILED DESCRIPTION

Described herein are approaches to the use of a microwave-assistedmagnetic recording (MAMR) head to improve the signal-to-noise ratio(SNR) over the entire region from the inner diameter to the outerdiameter of the disk, for example, for use in a shingled magneticrecording (SMR) hard disk drive (HDD). In the following description, forthe purposes of explanation, numerous specific details are set forth inorder to provide a thorough understanding of the embodiments of theinvention described herein. It will be apparent, however, that theembodiments of the invention described herein may be practiced withoutthese specific details. In other instances, well-known structures anddevices are shown in block diagram form in order to avoid unnecessarilyobscuring the embodiments of the invention described herein.

Physical Description of Illustrative Embodiments of the Invention

Embodiments of the invention may be used in the context of a magneticwriter for a hard-disk drive (HDD). In accordance with an embodiment ofthe invention, a plan view illustrating an HDD 100 is shown in FIG. 1.FIG. 1 illustrates the functional arrangement of components of the HDDincluding a slider 110 b that includes a magnetic-reading/recording head110 a. Collectively, slider 110 b and head 110 a may be referred to as ahead slider. The HDD 100 includes at least one head gimbal assembly(HGA) 110 including the head slider, a lead suspension 110 c attached tothe head slider, and a load beam 110 d attached to the lead suspension110 c. The HDD 100 also includes at least one magnetic-recording media120 rotatably mounted on a spindle 124 and a drive motor (not shown)attached to the spindle 124 for rotating the media 120. The head 110 aincludes a write element and a read element for respectively writing andreading information stored on the media 120 of the HDD 100. The media120 or a plurality (not shown) of disks may be affixed to the spindle124 with a disk clamp 128.

The HDD 100 further includes an arm 132 attached to the HGA 110, acarriage 134, a voice-coil motor (VCM) that includes an armature 136including a voice coil 140 attached to the carriage 134; and a stator144 including a voice-coil magnet (not shown). The armature 136 of theVCM is attached to the carriage 134 and is configured to move the arm132 and the HGA 110 to access portions of the media 120 being mounted ona pivot-shaft 148 with an interposed pivot-bearing assembly 152. In thecase of an HDD having multiple disks, or platters as disks are sometimesreferred to in the art, the carriage 134 is called an “E-block,” orcomb, because the carriage is arranged to carry a ganged array of armsthat gives it the appearance of a comb.

With further reference to FIG. 1, in accordance with an embodiment ofthe present invention, electrical signals, for example, current to thevoice coil 140 of the VCM, write signal to and read signal from the head110 a, are provided by a flexible interconnect cable 156 (“flex cable”).Interconnection between the flex cable 156 and the head 110 a may beprovided by an arm-electronics (AE) module 160, which may have anon-board pre-amplifier for the read signal, as well as otherread-channel and write-channel electronic components. The AE 160 may beattached to the carriage 134 as shown. The flex cable 156 is coupled toan electrical-connector block 164, which provides electricalcommunication through electrical feedthroughs (not shown) provided by anHDD housing 168. The HDD housing 168, also referred to as a casting,depending upon whether the HDD housing is cast, in conjunction with anHDD cover (not shown) provides a sealed, protective enclosure for theinformation storage components of the HDD 100.

With further reference to FIG. 1, in accordance with an embodiment ofthe present invention, other electronic components (not shown),including a disk controller and servo electronics including adigital-signal processor (DSP), provide electrical signals to the drivemotor, the voice coil 140 of the VCM and the head 110 a of the HGA 110.The electrical signal provided to the drive motor enables the drivemotor to spin providing a torque to the spindle 124 which is in turntransmitted to the media 120 that is affixed to the spindle 124 by thedisk clamp 128; as a result, the media 120 spins in a direction 172. Thespinning media 120 creates a cushion of air that acts as an air-bearingon which the air-bearing surface (ABS) of the slider 110 b rides so thatthe slider 110 b flies above the surface of the media 120 without makingcontact with a thin magnetic-recording medium in which information isrecorded.

The electrical signal provided to the voice coil 140 of the VCM enablesthe head 110 a of the HGA 110 to access a track 176 on which informationis recorded. Thus, the armature 136 of the VCM swings through an arc 180which enables the HGA 110 attached to the armature 136 by the arm 132 toaccess various tracks on the media 120. Information is stored on themedia 120 in a plurality of stacked tracks (not shown) arranged insectors on the media 120, for example, sector 184. Correspondingly, eachtrack is composed of a plurality of sectored track portions, forexample, sectored track portion 188. Each sectored track portion 188 iscomposed of recorded data and a header containing a servo-burst-signalpattern, for example, an ABCD-servo-burst-signal pattern, informationthat identifies the track 176, and error correction code information. Inaccessing the track 176, the read element of the head 110 a of the HGA110 reads the servo-burst-signal pattern which provides aposition-error-signal (PES) to the servo electronics, which controls theelectrical signal provided to the voice coil 140 of the VCM, enablingthe head 110 a to follow the track 176. Upon finding the track 176 andidentifying a particular sectored track portion 188, the head 110 aeither reads data from the track 176 or writes data to the track 176depending on instructions received by the disk controller from anexternal agent, for example, a microprocessor of a computer system.

FIG. 2 is an air bearing surface (ABS) view of a shingled magneticrecording (SMR) head having a spin torque oscillator (STO), according toan embodiment of the invention. SMR head 200 comprises a main(recording) pole 202 and side gaps 208 a and 208 b between main pole 202and side shields 206 a and 206 b, respectively. SMR head 200 furthercomprises an STO 204 formed between the main pole 202 and a trailingshield 210. In conformity with SMR recording, the width of the main pole202 is wider than the width of the STO 204. The ratio of the widths ofthe main pole 202 and the STO 204 is typically optimized according tothe combination with the medium and/or the recording density. The STO204 is arranged offset from the center of the main pole 202 in thecross-track direction, in a particular offset direction 205. With thisstructure, the side gap 208 a is the same width as the side gap 208 b.

FIG. 3 is a schematic diagram illustrating the arrangement of arecording track and write head when using an SMR head having a STO, suchas SMR head 200 of FIG. 2, at (a) an inner diameter region, (b) a middlediameter region, and (c) an outer diameter region, according to anembodiment of the invention. For a non-limiting example, the innerdiameter may be where the radius of the disk is approximately 14.2 mm,the middle diameter may be where the radius of the disk is approximately21.5 mm, and the outer diameter may be where the radius of the disk isapproximately 29.6 mm.

Overwriting is usually done by the drive used in the SMR recordingsystem, either to the left or right of the main pole, depending on theradial position of the disk. That is, depending on the radial positionof the disk, the right side is overwritten leaving the portion writtento the left of the main pole, or the left side is overwritten leavingthe portion written to the right of the main pole.

As shown in FIG. 3( b), at the middle diameter of the disk, therecording head and the recording track are arranged in parallel. Withthis arrangement, the edge of the track is overwritten so as to leavethe portion recorded on the STO side, and this arrangement typicallyresults in a high SNR recording. As shown in FIG. 3( c), at the outerdiameter of the disk, the recording head is arranged at a skew angle tothe recording track. This arrangement also typically results in a highSNR recording and there is little deterioration in the SNR in the casein which the track edge is overwritten in a manner leaving the portionrecorded on the STO side (referred to as “clean edge writing”).

As shown in FIG. 3( a), at the inner diameter of the disk, the recordinghead is arranged at a skew angle to the recording track in the oppositedirection as on the outer-diameter side. In the case of overwriting in amanner leaving the portion recorded on the STO side (the right handschematic of FIG. 3( a)), the magnetic field on the leading edge side ofthe main pole 202 (FIG. 2) protrudes on the recording track side(referred to as “dirty edge writing”). Consequently, the SNR of thetrack before overwriting is reduced. The SNR after overwriting is alsoreduced because the magnetic field is applied to the portion of thetrack that should be remaining after overwriting one cycle earlier.Although the SNR is not reduced by the magnetic field on the leadingside of the main pole 202 (FIG. 2) in the case of overwriting the edgeof the track in a manner leaving the portion recorded on the sidewithout the STO (clean edge writing, with reference to the left handschematic of FIG. 3( a)), the assist effect of the STO 204 (FIG. 2)cannot be used and the SNR is greatly reduced compared to the middlediameter.

Introduction

The greater the strength of the AC magnetic field generated by the STOand the greater the assist gain in SNR, the more that the direction ofmagnetization of the field generation layer, which is the source of theAC magnetic field within the structure of an STO, is arranged in onedirection within the plane. The narrower the width of the STO, theeasier it is to arrange magnetization of the field generation layer inone direction. Therefore, the width of the STO in a MAMR head may be ofthe same order as the effective track width. When the width of the STOis narrower than the effective track width, an AC magnetic field cannotbe applied to the entire track width and produces little assist gain.Furthermore, when the width of the STO is wider than the effective trackwidth, the strength of the AC magnetic field is reduced.

In the case of recording while overwriting one side of a track in theSMR recording system, the width of the STO should be about the same asthe effective track width in order to apply an AC magnetic field to theentire effective track width after overwriting. Therefore, the width ofthe STO is preferably narrower than the width of the main pole, and theSTO is preferably shifted either left or right with respect to the mainpole.

As discussed, depending on the radial position of the disk, in an SMRrecording system the right side is overwritten leaving the portionwritten to the left of the main pole, or the left side is overwrittenleaving the portion written to the right of the main pole. Hence,overwriting in a manner leaving the STO side in a certain region of adisk obtains assist gain by the STO in the case of SMR recording using arecording head having an STO offset from the center of the main pole,but this means overwriting the side opposite to the STO in anotherregion, causing loss of assist gain. Thus, the conventional combinationof MAMR and SMR is problematic in that it does not obtain the assistgain by MAMR over the entire disk, and so does not obtain a high SNRover the entire disk.

MAMR Head with Asymmetric Side Gap for SMR

FIG. 4 is an ABS view of an SMR head having an STO, according to anembodiment of the invention. SMR head 400 comprises a main (recording)pole 402, side gap 408 a and side gap 408 b between main pole 402 andside shields 406 a and 406 b, respectively. SMR head 400 furthercomprises an STO 404 formed between the main pole 402 and a trailingshield 410. In conformity with SMR recording, the width of the main pole402 is wider than the width of the STO 404. The ratio of the widths ofthe main pole 402 and the STO 404 is typically optimized according tothe combination with the medium and/or the recording density. The STO404 is arranged offset from the center of the main pole 402 in thecross-track direction, in a particular offset direction 405.

In the structure of SMR head 200 of FIG. 2, the side gap 208 a is thesame width as the side gap 208 b. For example, the side gap in thisstructure may be approximately 80 nm on both sides. By contrast,according to the embodiment illustrated with SMR head 400 of FIG. 4, theside gap 408 a on the side without the STO is narrower than the side gap408 b on the side with the STO. For a non-limiting example, the width ofthe main pole may be approximately 80 nm, the width of the STO may beapproximately 40 nm, and the gap width between the main pole and thetrailing shield may be approximately 25 nm, with the STO 404 offset fromthe center of the main pole to the outer-diameter side of the disk adistance of approximately 25 nm.

FIG. 5 is a diagram illustrating the arrangement of a recording trackand write head when using an SMR head having an STO as illustrated inFIG. 4, at (a) an inner diameter region, (b) a middle diameter region,and (c) an outer diameter region, according to an embodiment of theinvention. For a non-limiting example, the inner diameter may be wherethe radius of the disk is approximately 14.2 mm, the middle diameter maybe where the radius of the disk is approximately 21.5 mm, and the outerdiameter may be where the radius of the disk is approximately 29.6 mm.

As discussed, overwriting is usually done by the drive used in the SMRrecording system, either to the left or right of the main pole,depending on the radial position of the disk. That is, depending on theradial position of the disk, the right side is overwritten leaving theportion written to the left of the main pole, or the left side isoverwritten leaving the portion written to the right of the main pole.

The cases of FIG. 5( b) middle diameter region and FIG. 5( c) outerdiameter region are the same as when using a recording head such as SMRhead 200 (FIG. 2). However, in the case of FIG. 5( a) inner diameterregion, the recording head of the present invention overwrites the edgeof the track leaving the side without the STO. In such a scenario, thereis no assist effect by the STO. The magnetic field gradient in thecross-track direction is high, however, due to the narrow side gap,which can make the SNR of the recording track higher than when using arecording head such as SMR head 200. In the case of recording to leavethe side without the STO (see, e.g., the left hand schematic of FIG. 3(a)), recording may be charged or not charged through the STO, wherebynot charging has the advantage of reducing power consumption of thedrive.

FIG. 6 is an ABS view of an SMR head having an STO, according to anembodiment of the invention. The embodiment illustrated in FIG. 6 is thereverse of the embodiment illustrated in FIG. 4, in that the STO isshifted to the inner-diameter side of the disk and the side gap isnarrower on the outer-diameter side. SMR head 600 comprises a main(recording) pole 602, side gap 608 a and side gap 608 b between mainpole 602 and side shields 606 a and 606 b, respectively. SMR head 600further comprises an STO 604 formed between the main pole 602 and atrailing shield 610. In conformity with SMR recording, the width of themain pole 602 is wider than the width of the STO 604. The ratio of thewidths of the main pole 602 and the STO 604 is typically optimizedaccording to the combination with the medium and/or the recordingdensity. The STO 604 is arranged offset from the center of the main pole602 in the cross-track direction, in a particular offset direction 605.

With the structure of SMR head 200 of FIG. 2, the side gap 208 a is thesame width as the side gap 208 b. For example, the side gap in thisstructure may be approximately 80 nm on both sides. By contrast,according to the embodiment illustrated with SMR head 600 of FIG. 6, theside gap 608 b on the side without the STO is narrower than the side gap608 a on the side with the STO. For a non-limiting example, the width ofthe main pole may be approximately 80 nm, the width of the STO may beapproximately 40 nm, and the gap width between the main pole and thetrailing shield may be approximately 25 nm, with the STO 604 offset fromthe center of the main pole to the outer-diameter side of the disk adistance of approximately 25 nm.

FIG. 7 is a diagram illustrating the arrangement of a recording trackand write head when using an SMR head having an STO as illustrated inFIG. 6, at (a) an inner diameter region, (b) a middle diameter region,and (c) an outer diameter region, according to an embodiment of theinvention. In this case, as illustrated in FIG. 7, overwriting in themiddle diameter region in order to leave the STO side (clean edgewriting, using STO side in contrast to using no-STO side in FIG. 5structure) and overwriting in the inner diameter region in order toleave the STO side, (as with the FIG. 5 structure), and overwriting onthe outer-diameter side in order to leave the side without the STO(clean edge writing, using no-STO side in contrast to using STO side inFIG. 5 structure), can produce a higher SNR on the outer-diameter sidethan with the structure of a recording head such as SMR head 200 (FIG.2). Thus, the capacity of a hard disk drive can be increased in asimilar manner with SMR head 600 as with the embodiment of SMR head 400depicted in FIG. 4, due to high cross-track magnetic field gradient.

An Example MAMR Head Design with Asymmetric Side Gap for SMR

Research involving the relationships between the magnetic field gradientand the side gap in the cross-track direction (with no STO, or STO-off)and between the magnetic field strength and the side gap (in a scenarioin which the side gap is the same length on both sides) shows that themagnetic field gradient in the cross-track direction improves but thatthe recording magnetic field strength is reduced, however, as the sidegap becomes narrower. Therefore, the side gap is usually set as narrowas possible within a range at which sufficient magnetic field strengthis obtained for the recording density of the medium.

The size of a sufficient recording magnetic field strength variesdepending on the size of the flux reversal magnetic field of the medium,the space between the head and the medium, and the like. The magneticfield strength generated by the main pole varies depending on the shapeof the main pole, the shape of the shield, the trailing gap, therecording current, and the like. Therefore, the optimum side gap alsovaries depending on these factors. For a non-limiting example, the sidegap on the side without the STO (the side gap on the inner-diameterside) may be approximately 30 nm and the side gap on the STO side (theside gap on the outer-diameter side) may be approximately 100 nm, for aMAMR SMR head design such as SMR head 400 illustrated in FIG. 4. In thepresent example, the side gap on the side without the STO has beennarrowed to 30 nm, which increases the magnetic field gradient in thecross-track direction compared to the SMR head 200 of FIG. 2. Were theside gap on the STO side made equal to the side gap on the side withoutthe STO, the magnetic field strength would be insufficient. Therefore,widening the side gap on the STO side to 100 nm augments the magneticfield strength.

Further, research involving the relationship between the cross-trackmagnetic field gradient on the STO side and the side gap, with STO-on,shows that the effective magnetic field gradient on the STO side ishigher than when there is no STO (i.e., STO-off). The effective magneticfield gradient on the STO side is nearly constant even if the side gapvaries, indicating that the gradient of the magnetic field generated bythe STO prevails on the STO side. Therefore, even widening the side gapon the STO side from 80 nm to 100 nm in the present example does notdeteriorate the magnetic field gradient in the cross-track direction onthe STO side.

SMR Recording with a MAMR Head with Asymmetric Side Gap

The dependency of the SNR on the skew angle of the recording head wasassessed, in the case of overwriting leaving the portion recorded on theSTO side and in the case of overwriting leaving the portion recorded onthe side without the STO, for heads having a structure such as SMR head200 (FIG. 2) and the structure according to embodiments, such as SMRhead 400 of FIG. 4. The skew angle is zero degrees at the middlediameter of the disk, a positive angle on the inner-diameter side of thedisk, and a negative angle on the outer-diameter side of the disk.Although the SNR on the STO side is high at the outer and middlediameters, the SNR is reduced on the inner-diameter side, for both theSMR head 200 structure and the structure according to embodiments. Inthe case of the SNR on the side without the STO, the SNR issignificantly higher with the structure of the embodiments than with theSMR head 200 structure, on the OD side. Further in the case of the SNRon the side without the STO, the SNR is still higher (e.g., around 1 dB)with the structure of the embodiments than with the SMR head 200structure, on the ID side. Both are due at least in part due to thestructure of the embodiments having a higher cross-track magnetic fieldgradient on the side without the STO than the structure of SMR head 200.

Using either the left side or the right side of the recording head bythe drive may be selected in order to increase the SNR at each skewangle, i.e., at each radial position. Thus, according to an embodiment,a shingled magnetic recording head of the structure of the embodiments(e.g., SMR head 400 of FIG. 4) may be used to overwrite leaving the STOside in the disk region where the skew angle is less than around tendegrees, and to overwrite leaving the side without the STO in the diskregion where the skew angle is around ten degrees or greater. As aresult, the structure according to embodiments of the invention canincrease the SNR more than the SMR head 200 (FIG. 2) structure, in theregion where the skew angle is ten degrees or greater. Consequently,using a recording head having the structure according to embodiments canincrease the capacity of a hard disk drive.

For example, a hard disk drive electronic component (such as awrite-channel electronic component as described in reference to FIG. 1)is configured to execute one or more sequences of instructions which,when executed by one or more processors, causes the hard disk drive tooverwrite in the foregoing manner based on the region of the disk onwhich the drive is writing. The process logic embodied in the one ormore sequences of instructions may be implemented, for example, asanalog or digital hardware circuitry within the electronic component oras firmware instructions executed by a processor on board or separatefrom the electronic component.

MAMR Head with High Saturation Magnetization Material Side Shield

FIG. 8 is an ABS view of an SMR head having an STO, according to anembodiment of the invention. SMR head 800 comprises a main (recording)pole 802 and side gaps 808 a and 808 b between main pole 802 and sideshields 806 a and 806 b, respectively. SMR head 800 further comprises anSTO 804 formed between the main pole 802 and a trailing shield 810. Inconformity with SMR recording, the width of the main pole 802 is widerthan the width of the STO 804. The ratio of the widths of the main pole802 and the STO 804 is typically optimized according to the combinationwith the medium and/or the recording density. The STO 804 is arrangedoffset from the center of the main pole 802 in the cross-trackdirection, in a particular offset direction 805. In this embodiment, theside gap 808 a is the same width as the side gap 808 b.

According to the embodiment illustrated in FIG. 8, SMR head 800comprises a structure in which the region of the side shield 806 aopposing the side with the STO 804 comprises a material having highsaturation magnetization (B_(s). Making this region of the side shieldfrom a material having a higher B_(s) than the other portions of theshield, such as opposing side shield 806 b and trailing shield 810, mayimprove the cross-track gradient on the side without the STO, similarlyas with the embodiment of SMR head 400 (FIG. 4) which comprises a narrowside gap 408 a (FIG. 4). Consequently, the structure of SMR head 800 mayobtain a higher SNR than the structure of SMR head 200 (FIG. 2).

Further, the STO 804 may be arranged on the outer-diameter side of thedisk (as shown in FIG. 8) or on the inner-diameter side of the disk.Regardless of the side to which STO 804 is biased, the side shield onthe opposite side of STO 804 comprises the high saturation magnetizationmaterial.

Although only the side shield on the side without the STO is made from ahigh saturation magnetization material in SMR head 800 of FIG. 8, thesame or a similar high B_(s) material may also be used for the surfaceof the trailing shield 810 on the side opposite STO 804, according to anembodiment. Using a high B_(s) material in a region of the trailingshield 810 opposite the STO 804 may further improve the cross-trackgradient on the side without the STO 804.

FIG. 9 is an ABS view of an SMR head having an STO, according to anembodiment of the invention. SMR head 900 comprises a main (recording)pole 902 and side gaps 908 a and 908 b between main pole 902 and sideshields 906 a and 906 b, respectively. SMR head 900 further comprises anSTO 904 formed between the main pole 902 and a trailing shield 910. Inconformity with SMR recording, the width of the main pole 902 is widerthan the width of the STO 904. The ratio of the widths of the main pole902 and the STO 904 is typically optimized according to the combinationwith the medium and/or the recording density. The STO 904 is arrangedoffset from the center of the main pole 902 in the cross-trackdirection, in a particular offset direction 905.

According to the embodiment illustrated in FIG. 9, SMR head 900comprises a structure in which the side gap 908 a on the side withoutthe STO 904 is narrower than the side gap 908 b on the side with the STO904, and in which the region of the side shield 906 a opposing the sidewith the STO 904 comprises a material having high saturationmagnetization (B_(s)). The effects of the narrow side gap 908 a and thehigh B_(s) material of the side shield 906 a may improve the cross-trackgradient on the side without the STO 904. Consequently, the structure ofSMR head 800 may obtain a higher SNR than the structure of SMR head 200(FIG. 2).

Further, according to embodiments, the STO 904 may be arranged on theouter-diameter side of the disk (as shown in FIG. 9) or on theinner-diameter side of the disk. Regardless of the side to which STO 904is biased, the side shield on the opposite side of STO 804 comprises thehigh saturation magnetization material. Still further, the material ofthe side shield 906 b on the STO 904 side may be a high-B_(s) material,or a material having the same level of B_(s) as the other portions ofthe shield such as trailing shield 910.

In the foregoing specification, embodiments of the invention have beendescribed with reference to numerous specific details that may vary fromimplementation to implementation. Thus, the sole and exclusive indicatorof what is the invention, and is intended by the applicants to be theinvention, is the set of claims that issue from this application, in thespecific form in which such claims issue, including any subsequentcorrection. Any definitions expressly set forth herein for termscontained in such claims shall govern the meaning of such terms as usedin the claims. Hence, no limitation, element, property, feature,advantage or attribute that is not expressly recited in a claim shouldlimit the scope of such claim in any way. The specification and drawingsare, accordingly, to be regarded in an illustrative rather than arestrictive sense.

What is claimed is:
 1. A microwave-assisted magnetic recording (MAMR)head comprising: a magnetic writer main pole extending to an air bearingsurface; a shield wrapping around at least a portion of said main pole,said shield comprising a trailing shield at a trailing side of said mainpole and a side shield at each respective side of said main pole in across-track direction; a gap between said main pole and said shield,said gap comprising a trailing gap between said trailing shield and saidmain pole and a side gap between each respective side shield and saidmain pole; a spin torque oscillator (STO) element positioned betweensaid main pole and said trailing shield and offset in a particularoffset direction from a centerline of said main pole; and wherein thesaturation magnetization of the side shield positioned on the sideopposing said offset direction is higher than the saturationmagnetization of the side shield positioned on the side of said offsetdirection.
 2. The MAMR head of claim 1, wherein said STO element isoffset in an inner diameter (ID) direction; and wherein the saturationmagnetization of the side shield positioned at an outer diameter (OD)side of said main pole is higher than the saturation magnetization ofthe side shield positioned at an ID side of said main pole.
 3. The MAMRhead of claim 1, wherein said STO element is offset in an outer diameter(OD) direction; and wherein the saturation magnetization of the sideshield positioned at an inner diameter (ID) side of said main pole ishigher than the saturation magnetization of the side shield positionedat an OD side of said main pole.
 4. The MAMR head of claim 1, whereinthe side gap positioned on the side opposing said offset direction isnarrower than the side gap positioned on the side of said offsetdirection.
 5. The MAMR head of claim 1, wherein said STO element isoffset in an inner diameter (ID) direction; and wherein the side gappositioned at an outer diameter (OD) side of said main pole is narrowerthan the side gap positioned at an ID side of said main pole.
 6. TheMAMR head of claim 1, wherein said STO element is offset in an outerdiameter (OD) direction; and wherein the side gap positioned at an innerdiameter (ID) side of said main pole is narrower than the side gappositioned at an OD side of said main pole.
 7. The MAMR head of claim 1configured for shingled magnetic recording, wherein the maximum width ofsaid main pole at said air bearing surface is wider than a correspondingeffective recording track width.
 8. The MAMR head of claim 7, whereinthe width of said STO is narrower than the maximum width of said mainpole at said air bearing surface and is approximately equal to saidcorresponding effective recording track width.
 9. A hard disk drive,comprising: a head slider, comprising: a magnetic writer main poleextending to an air bearing surface; a shield wrapping around at least aportion of said main pole, said shield comprising a trailing shield at atrailing side of said main pole and a side shield at each respectiveside of said main pole in a cross-track direction; a gap between saidmain pole and said shield, said gap comprising a trailing gap betweensaid trailing shield and said main pole and a side gap between eachrespective side shield and said main pole; a spin torque oscillator(STO) element positioned between said main pole and said trailing shieldand offset in a particular offset direction from a centerline of saidmain pole; and wherein the saturation magnetization of the side shieldpositioned on the side opposing said offset direction is higher than thesaturation magnetization of the side shield positioned on the side ofsaid offset direction; a magnetic-recording disk rotatably mounted on aspindle; and a voice coil motor configured to move the head slider toaccess portions of the magnetic-recording disk.
 10. The hard disk driveof claim 9, wherein said STO element is offset in an inner diameter (ID)direction; and wherein the saturation magnetization of the side shieldpositioned at an outer diameter (OD) side of said main pole is higherthan the saturation magnetization of the side shield positioned at an IDside of said main pole.
 11. The hard disk drive of claim 9, wherein saidSTO element is offset in an outer diameter (OD) direction; and whereinthe saturation magnetization of the side shield positioned at an innerdiameter (ID) side of said main pole is higher than the saturationmagnetization of the side shield positioned at an OD side of said mainpole.
 12. The hard disk drive of claim 9, wherein the side gappositioned on the side opposing said offset direction is narrower thanthe side gap positioned on the side of said offset direction.
 13. Thehard disk drive of claim 9, wherein said STO element is offset in aninner diameter (ID) direction; and wherein the side gap positioned at anouter diameter (OD) side of said main pole is narrower than the side gappositioned at an ID side of said main pole.
 14. The hard disk drive ofclaim 9, wherein said STO element is offset in an outer diameter (OD)direction; and wherein the side gap positioned at an inner diameter (ID)side of said main pole is narrower than the side gap positioned at an ODside of said main pole.
 15. The hard disk drive of claim 9 configuredfor shingled magnetic recording, wherein the maximum width of said mainpole at said air bearing surface is wider than a corresponding effectiverecording track width.
 16. The hard disk drive of claim 15, wherein thewidth of said STO is narrower than the maximum width of said main poleat said air bearing surface and is approximately equal to saidcorresponding effective recording track width.